A study on the influence of doses nitrogen on salt concentration, yield, biological value, and chemical composition of butterhead lettuce, kale, and leafy celery was carried out under greenhouse conditions in 2006-2008. The experiment was set up as a completely randomized design. A single experimental unit consisted of one pot with a plant. Increasing rates of nitrogen in the form of ammonium nitrate (34% N): 0.3; 0.6; 0.9; 1.2 g N·dm^-3 of growing medium, were applied in all investigations, while the other macronutrients were the same for all plants. The obtained results revealed that the salt concentration in the growing medium depended both on the rate of nitrogen and the plant grown. Significantly lower crop yield was recorded when the highest nitrogen rate was applied (1.2 g N∙dm^-3), although this relationship was shown when there was high variation in EC in particular types of medium. It was found that excessive salt concentration in the growing medium due to increasing nitrogen rates significantly reduced vitamin C content in butterhead lettuce and leafy celery. An opposite relationship was observed for kale leaves. It was found that the protein levels in the tested plants increased with an increase in nitrogen rates. As compared to the lowest rate, the increase was 32.2% for butterhead lettuce, 30.6% for kale, and 41.2% for leafy celery.

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